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Pedestal Collector Transistor With Retarded Base

IP.com Disclosure Number: IPCOM000075677D
Original Publication Date: 1971-Oct-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Ghosh, HN: AUTHOR

Abstract

In this transistor a high collector-base impurity gradient is obtained by improving the base profile near the collector base junction. The improvement is a retarded base impurity profile in which the impurity gradient in the base region, adjacent the emitter, is substantially increased. This results in a lower base resistance, higher punch-through voltage, or a narrower base for a particular doping level resulting in a higher gain and a higher gain band with frequency.

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Pedestal Collector Transistor With Retarded Base

In this transistor a high collector-base impurity gradient is obtained by improving the base profile near the collector base junction. The improvement is a retarded base impurity profile in which the impurity gradient in the base region, adjacent the emitter, is substantially increased. This results in a lower base resistance, higher punch-through voltage, or a narrower base for a particular doping level resulting in a higher gain and a higher gain band with frequency.

As shown in A, an arsenic diffusion is made in wafer 10, resulting in a diffused region 12 having a surface concentration on the order of 1020 atoms per cc. Masking layer 14 is then removed and an N; epi layer 16 deposited on wafer 10. Masking layer 18 is then deposited diffusion window 19 formed therein, which has a substantially smaller area than the subcollector 12. An N-type impurity is then diffused through window 19 forming region 24 along with a P-type impurity forming region 26. The P-type impurity has a substantially greater diffusivity than the N-type impurity. As shown in D, the surface concentration of the N impurity is approximately 10/20/and the P type approximately 10/19/ atoms per cc. Typically, the impurities selected are arsenic and boron or arsenic and gallium.

Masking layer 18 is then removed and an upper N-type doped epitaxial layer 20 deposited. Base region 28 and emitter region 30 are then diffused from the surface, using conve...